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The Lodestar prospect in eastern Newfoundland contains significant concentrations of Au within sulfide-mineralized, polylithic, magmatic-hydrothermal breccias. The highest grade was 58.5 g/t Au from a grab sample of massive arsenopyrite. Selective samples of other sulfide phases in the breccia, such as pyrite, however, failed to produce any comparatively anomalous Au values. We conclude that Au at the Lodestar prospect is directly related to the arsenopyrite. Sulfide-bearing samples were investigated using a variety of analytical techniques. Recent developments of in situ laser-ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) techniques have provided important insights into trace-element distributions in minerals. ICP-MS analyses were undertaken to determine whether Au is distributed homogeneously in sulfides, particularly arsenopyrite, or is contained as micronuggets. The LAM-ICP-MS results demonstrate that the Lodestar arsenopyrite contains Au concentrations that attain 201 g/t. Gold is "homogeneously" (i.e., no nugget effect) contained within the structure of arsenopyrite. Other sulfide phases, such as pyrite and chalcopyrite, contain very low levels of Au. Gold contents in arsenopyrite from individual samples, and even within individual crystals, do vary, presumably related to arsenic concentrations. As gold was not observable by any of the other micro-analytical techniques, it must be chemically bound in the arsenopyrite structure, thereby classifying it as "invisible" gold.

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